1. Field of the Invention
The present invention relates to a semiconductor light-emitting device, and more particularly to a semiconductor light-emitting device having a semiconductor light-emitting element (hereinafter also referred to as a light-emitting element) bonded to a substrate by flip-chip bonding using an anisotropically conductive adhesive.
2. Description of the Prior Art
For example, some blue or green light-emitting diode (LED) elements (light-emitting elements) have a structure in which a pair of electrodes, namely a positive and a negative electrode, are formed on the same surface. As shown in FIG. 5, when this type of LED element 1 is mounted on a substrate 2, first the LED element 1 is fixed on the substrate 2 with an adhesive (not shown) such as silver paste, and then a pair of electrodes 12 and 12′ formed on the top surface of the LED element 1 are connected, with bonding wires W and W′, to wiring electrodes 21 and 21′ formed on the substrate 2. In a semiconductor light-emitting device fabricated in this way, while the light emitted upward from the light-emitting layer (active layer) of the LED element 1 exits therefrom through the top surface thereof, the light emitted downward from the light-emitting layer of the LED element 1 is diffusively reflected from the silver paste laid under the bottom surface thereof, so that part of this light is reflected upward so as to exit from the LED element 1 through the top surface thereof.
In the conventional semiconductor light-emitting device structured as described above, on the top surface of the LED element 1, there is formed a current diffusion film 13 as well as the electrodes 12 and 12′. These intercept part of the emitted light, resulting in low light extraction efficiency. Moreover, the bonding wires need to be bent with their sharpest permissible or a less sharp curvature. This makes it difficult to make the device slim.
One way to overcome these inconveniences is, as shown in FIG. 6, to form bumps B and B′ on the wiring electrodes 21 and 21′ so that, by way of those bumps B and B′, the LED element 1 is bonded to the wiring electrodes 21 and 21′ on the substrate 2 by flip-chip bonding. In this structure, there is nothing that intercepts the emitted light on the top surface of the LED element 1, i.e., the surface thereof through which the light exits therefrom. This helps increase light extraction efficiency. Moreover, the disuse of bonding wires makes it possible to make the device slim.
However, flip-chip bonding using bumps results in low mechanical strength around where bonding is performed, and thus leads to low reliability. Moreover, bumps need to be formed accurately in predetermined positions on the electrodes of each light-emitting element or on wiring electrodes formed on the substrate. This lowers the productivity and thus the yield of the device. Furthermore, the thickness of bumps themselves is disadvantageous for further slimming-down.